Influences of tillage system, climate, and soils on the demand for topsoil in northcentral Oregon wheat production

Graduation date: 1986Soil erosion research in the fields of agronomy, soils science\ud and mechanics, agricultural engineering, hydrology, climatology, and\ud other scientific disciplines has economic dimensions. In general,\ud measurable and, at times, significant economic effects are\ud associated with the effects of erosion in the other disciplines.\ud Interactions between climate, soils, hydrology, and tillage\ud practices are incorporated into a stochastic simulation model that\ud considers twenty six combinations of five tillage systems, three\ud initial soil depths, two soil associations, two slope classes, and\ud two annual precipitation levels over one hundred years. The model\ud endogeneously determines stochastic annual soil loss. Yield is a\ud function of varying soil depth and technological advance. The model\ud maximizes the wheat producer's objective, 100-year discounted quasi-rents\ud from wheat production. Cumulative or total rent distributions\ud that derive from alternative tillage systems in the different\ud ecological circumstances are compared under stochastic dominance. In low rainfall, shallow soil areas, annual tillage systems were\ud preferred to fallow ones, while conservation tillage dominated plow\ud tillage. In high rainfall areas, for either shallow or deep soil,\ud conservation tillage dominated plow tillage, while plow tillage\ud dominated no-till.\ud Manipulation of the tillage-associated rent distributions\ud permitted the estimation of value-of-marginal product or willingness\ud to pay curves (ordinary, profit-maximizing, input demand curves)\ud that express the depth of soil as a function of its economic worth.\ud Properties of these curves are discussed.\ud Comparison of expected total returns and marginal returns to\ud topsoil increments under alternative tillage systems in defined\ud ecological circumstances paralleled the stochastic dominance\ud results. Rankings of tillage systems by expected total returns\ud differed between ecological areas and differed from rankings by\ud marginal returns.\ud Regardless of tillage system or ecological circumstances, the\ud economic worth of each added soil increment diminished.\ud The experiment showed that differential rates of soil loss\ud associated with different tillage systems influence the decision to\ud continue using or to initially invest in alternative tillages, and\ud also influence the economically rational wheat producer's\ud willingness to incur costs associated with soil conservation.\ud Total and marginal rents associated with single tillages were\ud found to vary greatly across ecological circumstances. The ability and the willingness to invest in soil conservation were somewhat\ud divorced. This result has significance for soil conservation\ud targeting